The invention relates to a variable pressure oil pump for use with an engine, such as an internal combustion engine of a motor vehicle.
A typical motor vehicle includes an internal combustion engine and a lubrication system for providing oil to various lubrication locations of the engine. Such lubrication locations include sleeve bearings that support a rotating shaft, such as a camshaft. The oil produces a viscous friction drag on the rotating shaft, and the frictional drag converts mechanical energy from the shaft into heat energy within the oil. To prevent the oil from overheating within the bearings, the bearings are continually provided pressurized, lower temperature oil from an oil pump of the lubrication system. The pressurized, lower temperature oil is forced into the bearings and displaces heated oil out of the bearings.
When the engine is cold, such as during a cold start, however, the oil in the bearings is cold and the viscosity of the oil is high. As a result, it is not desirable to replace this oil with pressurized, low temperature oil.
Systems have been developed to vary oil pressure of oil provided to bearings of an internal combustion engine. U.S. Pat. No. 5,339,776, for example, discloses a lubrication system that includes an oil pump that draws oil from an oil sump, and a bypass valve that is capable of diverting oil supplied by the oil pump back into the oil sump without routing the oil to the bearings. Because high pressure oil is dumped back into the sump, however, aeration of the oil may occur. Furthermore, the oil dumped back into the sump will likely experience significant heat loss.
The present invention addresses the shortcomings of the prior art by providing a variable pressure oil pump assembly that can vary outlet oil pressure based on one or more operating conditions. Furthermore, outlet oil pressure may be varied without diverting high pressure oil into an oil sump.
Under the invention, a variable pressure oil pump assembly for use with a vehicle having a controller includes a pump body having an inlet, an outlet, a valve chamber, a first passage disposed between the inlet and the valve chamber, and a second passage disposed between the outlet and the valve chamber. The assembly further includes a pressure relief valve subassembly having a movable plunger that is disposed at least partially in the valve chamber for controlling flow of oil through the valve chamber so as to control outlet oil pressure at the outlet. A plunger adjustment mechanism is associated with the valve subassembly and adapted to communicate with the controller. The plunger adjustment mechanism is operable to control movement of the plunger based on control signals provided by the controller.
The plunger adjustment mechanism may be any suitable mechanism that is configured to affect movement of the plunger. For example, the plunger adjustment mechanism may include a solenoid subassembly connected to the pump body and adapted to be electrically connected to the controller. With such a configuration, when the solenoid subassembly is energized, the solenoid subassembly draws the plunger toward an open position for allowing oil to flow through the valve chamber.
In another embodiment of the invention, the plunger has an enlarged head having first and second sides, and the plunger adjustment mechanism includes a housing connected to the pump body and defining a housing chamber that receives the enlarged head. Furthermore, the housing including first and second apertures. The first aperture is in fluid communication with the first side of the enlarged head. The second aperture is in fluid communication with the second side of the enlarged head and is further connected to the inlet. In addition, the plunger adjustment mechanism includes a solenoid valve adapted to be electrically connected to the controller and further connected to the first aperture, the inlet and the outlet. When the solenoid valve is energized, the first aperture is exposed to the outlet oil pressure. When the solenoid valve is de-energized, the first aperture is exposed to inlet oil pressure.
In yet another embodiment of the invention, the plunger has an enlarged head having first and second sides, and the plunger adjustment mechanism includes a housing connected to the pump body and defining a housing chamber that receives the enlarged head. Furthermore, the housing includes first and second apertures. The first aperture is in fluid communication with the first side of the enlarged head. The second aperture is in fluid communication with. the second side of the enlarged head and is further connected to the inlet so as to expose the second side of the enlarged head to inlet oil pressure. In addition, the plunger adjustment mechanism includes an additional pump connected between the first aperture and the inlet and adapted to be electrically connected to the controller. When the additional pump is not activated, the additional pump provides the inlet oil pressure to the first aperture. When the additional pump is activated, the additional pump provides oil pressure to the first aperture that is greater than the inlet oil pressure.